Known charge generating materials having sensitivity in the near infrared region which can be used in electrophotographic photoreceptors include squarylium pigments, bisazo pigments, and phthalocyanine pigments. Of these materials, phthalocyanine pigments have recently been attracting particular attention because of their high sensitivity, and various species thereof having different crystal forms have hitherto been proposed for use as a charge generating material of electrophotographic photoreceptors. For example, chloroindium phthalocyanine having a .beta.-crystal form is disclosed in JP-A-59-155851 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). JP-A-60-59355 reports that chloroindium phthalocyanine having a specific crystal form is effective as a charge generating material. Further, JP-A-1-221459 describes that gallium phthalocyanine having a specific crystal form is also effective as a charge generating material.
JP-A-2-170166 and JP-A-2-280169 disclose that a mixed crystal of two or more species of phthalocyanines or a simple mixture of two or more species of phthalocyanine crystals is useful as a charge generating material of an electrophotographic photoreceptor.
However, a mixed crystal of a halogenated indium phthalocyanine and a halogenated gallium phthalocyanine has not yet been reported.
While the above-described known phthalocyanine species and mixed crystals thereof are useful as a charge generating material, all of them are still unsatisfactory. For example, the chloroindium phthalocyanine having a .beta.-crystal form disclosed in JP-A-59-155851 supra exhibits very high sensitivity but is still insufficient in dark decay, stability on repeated use, crystal form stability in a coating composition, and dispersibility in a coating composition. In order to settle these problems, it has been proposed to incorporate a small amount of a substituted phthalocyanine as described, e.g., in JP-A-3-9962, JP-B-55-27583, and JP-B-54-44684 (the term "JP-B" as used herein means an "examined published Japanese patent application"). In this case, however, since a substituted phthalocyanine incorporated is markedly different from unsubstituted phthalocyanine in crystal form, mixing them gives rise to another problem, such as reduction in electrophotographic characteristics.